Cass, I'm glad you asked. That was my Second thought, and I was trying with all my might not to ask! But especially the IRS clinches it for me.

 

Glyn
Agree the narrow 8 bar MK1 grille would be wrong on this car.
The later 14 bar MK1 grille would suit and it does not have the MK2 centre bar.

 

Like this. Agree wholeheartedly. From Aus. as well.

 

Front end style MK1, MK2, unique S-Type

 

The grill I show above is the wide 3.4 Mk1 grill. For better cooling.

 

Mk1 had 2 grill styles.

 

The 2.4 MK1 had the narrow 8 bar grille but with the introduction of the 3.4 it needed a larger intake area.
Asfar as I can ascertain this wider grille came in about August 1957.
The narrow grill 2.4 cars are quite scarce and bring in high prices.
An acquaintance has a narrow grille car with a 3.8 engine, MOD, and MK2 disc brakes on the front. It has some modifications to the radiator for more exposure below the car.
He really likes it and that is saying something when his stable includes Aston Martin DB5, XK140, E types and Bentleys.

 

Early grills were castings.

 

There is disagreement between the scribes on the launch of the wider grill. I think you have it about right. One thing we do know is that it was later than Lyons wanted for the USA power hungry market.